1. Field of the Invention
The present invention generally relates to an apparatus and method for transferring packets switched among a plurality of network segments, particularly to a technique for acquiring packets in the state where stealth characteristics are secured.
2. Description of the Related Art
In order to switch packets among a plurality of network segments (simply denoted as segments), for example, a packet transfer apparatus (packet relay apparatus) such as a router is generally provided on a computer network.
The packet transfer apparatus generally includes a computer as a main component so that some software (program and data) is used for operating the computer. Therefore, in the packet transfer apparatus, it is necessary to update a program or data included in the existing software.
Such a method of updating software is generally to access a server connected to, for example, Internet and to download and acquire an update file from the server. Thereby, the packet transfer apparatus can easily and rapidly acquire an update file to realize update of the software.
In packet transfer apparatuses in recent years, some apparatuses have a function of operating as a network protect system for preventing malicious accesses from, for example, hackers.
There is a case where such a packet transfer apparatus accesses a server as described above, and acquires an update file for updating software of the system. In this case, the packet transfer apparatus transmits the unique address (IP address and the like) on the network. Therefore, there is a possibility that the presence of the packet transfer apparatus is recognized by other devices on the network. Particularly, if the presence as the network protect system is recognized by the third party, it is not preferable that there occurs a situation the apparatus is easy to be attacked by hackers.
In order to eliminate security problems as described above, there is a method of reading an update file from a local storage medium such as a floppy disk or CD-ROM without accessing files on the network. Further, this is a method of transferring the update file from a computer serial-connected with the packet transfer apparatus. However, such a method is remarkably inefficient since complicated works are required as compared with convenience of the network capable of easily and rapidly acquiring an update file.
Therefore, it is desirable for a device on a networks, such as the packet transfer apparatus, to acquire an update file from the network. For example, on the network of TCP/IP protocol, a communication party can be recognized by a MAC (media access control) address, an IP (internet protocol) address, and a port number.
Therefore, when a unique address including the MAC address and the IP address is not assigned, the device such as the packet transfer apparatus on the network cannot perform communication on the network. However, it is possible to acquire and transfer all packets passing on the network to designated destinations instead of that the presence of the apparatus is not known by other devices on the network. Characteristics capable of concealing the presence of the apparatus from other devices on the network is called stealth characteristics.
However, a device on a network, such as the packet transfer apparatus, cannot communicate with any other device on the network if stealth characteristics that prohibit the transmission of the unique address are secured. In this case, an update file cannot be acquired from the devices.